Air distillation method with argon production and the corresponding air distillation unit

ABSTRACT

A method and apparatus for air distillation which makes it possible to deliver relatively large flow rates of oxygen-enriched and nitrogen-enriched fluid at a low cost, is provided. The apparatus has at least two double distillation columns and at least two argon columns that operate in parallel. The argon-enriched fluid which is formed are then mixed downstream of the argon columns, and directed through a common compressor, deoxygenation unit, or drying unit, and more than one of which may be common to both streams.

[0001] The present invention relates to an air distillation method, of the type comprising the steps of:

[0002] distilling air in at least one double distillation column in order to form at least a first oxygen-enriched fluid and a first nitrogen-enriched fluid, the double distillation column comprising a higher-pressure column and a lower-pressure column,

[0003] drawing off an argon-rich fluid from the lower-pressure column,

[0004] distilling the argon-rich fluid in at least one argon column in order to form an argon-enriched fluid and a second oxygen-enriched fluid,

[0005] compressing the argon-enriched fluid in at least one compressor,

[0006] reacting hydrogen with the oxygen contained in the compressed fluid, in at least one deoxygenation unit, in order to deoxygenate it while producing water,

[0007] passing the deoxygenated fluid through at least one drying unit in order to dry it, and

[0008] distilling the dried fluid in at least one denitrogenation column in order to form argon and a second nitrogen-enriched fluid.

[0009] Such a method is described in EP-A-0509871.

[0010] In a method of the aforementioned type, the first oxygen-enriched fluid is, for example, impure oxygen used for the gasification of charcoal in order to form a fuel supplied to a gas turbine.

[0011] Other applications require very large quantities of oxygen.

[0012] It is therefore desirable to provide air distillation plants which have high capacities.

[0013] However, it is also expedient to ensure that the overall costs associated with the operation of these plants are low.

[0014] It is therefore an object of the invention to provide an air distillation method of the aforementioned type, which makes it possible to deliver relatively large flow rates of a first oxygen-enriched fluid and/or a first nitrogen-enriched fluid, and the implementation of which entails low costs.

[0015] To this end, the invention relates to a method of the aforementioned type, characterized in that at least two double distillation columns and at least two argon columns which operate in parallel are used for distilling air, while forming at least two argon-enriched fluids, and in that the argon-enriched fluids are mixed downstream of the two argon columns, and in that at least one element selected from the group consisting of: the compressor, the deoxygenation unit and the drying unit, is a common element which is used in order to compress or deoxygenate or dry the mixed fluids together.

[0016] According to particular embodiments, the method may comprise one or more of the following characteristics, taken individually or in any technically feasible combinations:

[0017] all the mixed fluids are sent to a single common element selected from the group consisting of: the compressor, the deoxygenation unit and the drying unit,

[0018] a common element is the deoxygenation unit, in which hydrogen is reacted with the mixed fluids in order to deoxygenate them together while producing water,

[0019] a common element is the drying unit, through which the mixed fluids are passed in order to dry them together,

[0020] the drying unit comprises a device for drying by adsorption,

[0021] the drying unit comprises a phase separator,

[0022] a common element is the compressor, in which the mixed fluids are compressed together,

[0023] the mixed fluids are heated together in a common heat exchanger upstream of the compressor,

[0024] the dried fluids are cooled together in a common heat exchanger downstream of the drying unit,

[0025] the mixed fluids are heated upstream of the compressor, and the dried fluids are cooled downstream of the drying unit, in the same common heat exchanger,

[0026] a dedicated denitrogenation column, in which the respective deoxygenated and dried fluid is distilled, is used for each double distillation column and each argon column.

[0027] The invention also relates to an air distillation plant comprising:

[0028] at least one double distillation column for distilling air while forming at least a first oxygen-enriched fluid and a first nitrogen-enriched fluid, the double distillation column comprising a higher-pressure column and a lower-pressure column,

[0029] means for drawing off an argon-rich fluid from the lower-pressure column,

[0030] at least one argon column for distilling the argon-rich fluid while forming an argon-enriched fluid and a second oxygen-enriched fluid,

[0031] at least one compressor for compressing the argon-enriched fluid,

[0032] at least one deoxygenation unit for reacting hydrogen with the oxygen contained in the compressed fluid, in order to deoxygenate it while producing water,

[0033] at least one drying unit for the deoxygenated fluid to be passed through in order to dry it, and

[0034] at least one denitrogenation column for distilling the dried fluid while forming argon and a second nitrogen-enriched fluid,

[0035] characterized in that it comprises at least two double distillation columns and at least two argon columns, designed to operate in parallel in order to distil air while forming at least two argon-enriched fluids, and in that the plant comprises means for mixing the argon-enriched fluids downstream of the two argon columns, and in that at least one element selected from the group consisting of: the compressor, the deoxygenation unit and the drying unit, is a common element designed to compress or deoxygenate or dry the mixed fluids together.

[0036] According to particular embodiments, the plant may comprise one or more of the following characteristics, taken individually or in any technically feasible combinations:

[0037] a common element is the deoxygenation unit, which is designed to react hydrogen with the mixed fluids in order to deoxygenate them while producing water,

[0038] a common element is the drying unit, which is designed for the mixed fluids to be passed through it in order to dry them together,

[0039] the drying unit comprises a device for drying by adsorption,

[0040] the drying unit comprises a phase separator,

[0041] a common element is the compressor, which is designed in order to compress the mixed fluids together,

[0042] the plant comprises a common heat exchanger, arranged upstream of the compressor, for heating the mixed fluids together,

[0043] the plant comprises a common heat exchanger, arranged downstream of the drying unit, for cooling the dried fluids together,

[0044] the plant comprises a single common heat exchanger, for heating the mixed fluids upstream of the compressor and cooling the mixed and dried fluids downstream of the drying unit,

[0045] for each double distillation column and each argon column, the plant comprises a dedicated denitrogenation column for the respective deoxygenated and dried fluid to be distilled in it.

[0046] The invention will be understood more clearly on reading the following description, which is given solely by way of nonlimiting example and refers to the appended drawings, in which:

[0047]FIG. 1 is a schematic view of an air distillation plant according to a first embodiment,

[0048]FIG. 2 is a partial schematic view of an air distillation plant according to a second embodiment of the invention.

[0049] In what follows, the concentrations given in the form of a percentage are molar concentrations.

[0050]FIG. 1 schematically illustrates an air distillation plant 1, which essentially comprises:

[0051] two air distillation systems 2A and 2B operating in parallel, and

[0052] a common deoxygenation and drying system 3 connected to the systems 2A and 2B.

[0053] The systems 2A and 2B have similar structures. Throughout what follows, the references used to denote the corresponding elements of these two systems will therefore be provided with the same reference number, followed either by the suffix A or by the suffix B. Owing to this similarity in structure, only the elements and the connections essential to system 2B have been represented in FIG. 1, and only the structure and function of system 2A will be described below.

[0054] The distillation system 2A essentially comprises:

[0055] a double distillation column 6A, which itself comprises a higher-pressure column 8A, a lower-pressure column 10A and a vaporizer/condenser 12A for establishing heat-exchange communication between the head of the column 8A and the bottom of the column 10A,

[0056] a first auxiliary distillation column 14A, generally referred to as an argon column, this column 14A being provided with a head vaporizer/condenser 16A,

[0057] a second auxiliary column 18A, generally referred to as a denitrogenation column, this column being provided with a bottom vaporizer 20A and a head vaporizer/condenser 22A,

[0058] an air compressor 24A,

[0059] a unit 26A for purification of air by adsorption, and

[0060] a primary heat exchanger 28A and two auxiliary heat exchangers 30A and 32A.

[0061] The air to be distilled is compressed by the compressor 24A, purified by the unit 26A, cooled to near its dew point by the primary exchanger 28A, then introduced at the bottom of the column 8A.

[0062] “Rich liquid” LR (oxygen-enriched air) drawn off from bottom of column 8A, is supercooled in the auxiliary exchanger 30A then divided into two streams. A first of these streams has its pressure reduced in a valve 34A then is introduced at a first intermediate level of the column 10A.

[0063] The second stream of rich liquid air LR is sent to the vaporizer/condenser 16A of the argon column 14A, where it is vaporized. This vaporized rich liquid LR is returned to a second intermediate level of the lower-pressure column 10A. This second intermediate level is arranged below the first intermediate level.

[0064] Impure (or residual) nitrogen NR is taken from the head of the lower-pressure column 10A then heated, first through the auxiliary heat exchanger 30A and secondly through the primary heat exchanger 28A.

[0065] “Lean liquid” LP (substantially pure nitrogen) taken from the head of the column 8A is divided into two streams, a first of which is supercooled in the auxiliary exchanger 30A, then has its pressure reduced in a valve 36A and is finally introduced at the top of the lower-pressure column 10A.

[0066] The second stream of lean liquid LP is sent to the head vaporizer/condenser 22A of the denitrogenation column 18A, where it is vaporized. The vaporized lean liquid LP coming from the vaporizer/condenser 22A is mixed with the impure nitrogen NR upstream of the exchanger 30A.

[0067] Oxygen gas OG is drawn off from the bottom of the lower-pressure column 10A is then heated through the primary heat exchanger 28A, at the outlet of which it is distributed via a production pipe 38A as a first distillation product. It may be pure oxygen, for example, that is to say oxygen with a purity of between 99 and 99.8%.

[0068] A gas containing mainly oxygen and argon is drawn off via a pipe 39A from a third intermediate level of the lower-pressure column 10A. This third intermediate level, located below the second intermediate level, conventionally corresponds to the argon peak formed by the profile of the argon composition in the gas mixture inside the column 10A. The gas which is drawn off thus contains, for example, about 90% oxygen, 10% argon and less than 2000 ppm nitrogen. It is therefore an argon-rich gas compared with air, which contains only about 0.9% argon.

[0069] This argon-rich gas is introduced at the bottom of the argon column 14A. This column 14A distils this gas, and its bottom produces a liquid mainly composed of oxygen which is returned via a pipe 40A to the third intermediate level of the lower-pressure column 10A. The head of the column 14A produces an argon-enriched gas which contains for the most part argon—typically 95%, nitrogen—typically 3%, and oxygen—typically 2%.

[0070] The reflux in the column 14A is carried out by condensing the head gas in the vaporizer/condenser 16A then returning this condensed gas into the column 14A. This condensation is ensured by the vaporizing of some of the rich liquid LR which was previously supercooled, as described above.

[0071] The argon-enriched gas coming from the argon column 14A is heated in the auxiliary exchanger 32A then mixed at a point 41 with the argon-enriched gas coming from the argon column 14B, which has previously been heated in an auxiliary exchanger 32B.

[0072] The two gases mixed in this way then form a single stream, which is introduced into the deoxygenation and drying system 3.

[0073] This system 3 essentially comprises, connected in series:

[0074] a compressor 42,

[0075] a cooling device 44,

[0076] a deoxygenation unit 46,

[0077] a cooling device 48,

[0078] a drying unit 50, comprising a phase separator 51 and a device 52 for drying by adsorption.

[0079] The gas mixture is compressed by the compressor 42 then cooled in the device 44. Hydrogen is then added to the compressed and cooled mixture, by means of a single pipe 54, before introduction into the deoxygenation unit 46.

[0080] This deoxygenation unit 46 comprises a chemical reactor in the form of a metal vessel containing a catalyst bed. The oxygen contained in the compressed and cooled mixture reacts with the added hydrogen in order to form water.

[0081] The mixture deoxygenated in this way and containing water is then cooled in the device 48, then sent to the separator 51, which is for example a separator pot, where the liquid water contained in the mixture is eliminated. The gas coming from the separator 51 is then sent to the device 52 for drying by adsorption, which typically comprises alumina-filled bottles connected in parallel to the separator 51. The single gas stream coming from the separator 51 is sent alternately to one or other of the bottles, the bottle through which the stream does not flow being in a regeneration phase. The single gas stream coming from the unit 50 therefore essentially contains argon and nitrogen, the oxygen and the water having been eliminated.

[0082] This gas leaves the system 3 then is divided into two streams at a point 54, a first stream being sent to the distillation system 2A and a second stream being sent to the distillation system 2B. It will be noted that the flow rate of the stream sent to the system 2A or 2B, respectively, is substantially equal to the flow rate of argon and oxygen drawn off from the column 14A or 14B, respectively, via the corresponding enriched gas.

[0083] The gas stream returned to the unit 2A is cooled in the heat exchanger 32A then condensed in the bottom vaporizer 20A of the denitrogenation column 18A. The liquid obtained in this way has its pressure reduced in a valve 56A and is finally introduced at an intermediate level of the column 18A. The aforementioned condensation ensures the vaporization of the bottom liquid of the denitrogenation column 18A by the vaporizer 20A. The reflux in the column 18A is carried out by condensing its head gas in the vaporizer/condenser 22A. This condensation is ensured by vaporizing some of the lean liquid LP, as described above.

[0084] The head of the column 18A produces a gas containing for the most part nitrogen, which is transported via a pipe 57A in order to be mixed with the liquid vaporized by the vaporizer/condenser 22A, before this vaporized liquid LP is mixed with impure nitrogen NR.

[0085] A pipe 58A makes it possible to draw off pure liquid argon from the bottom of the denitrogenationdenitrogenation column 18A. This argon typically contains between 1 and 10 ppm oxygen and/or nitrogen.

[0086] The pipes 58A and 58B are connected to a common production pipe 60, in order to mix the two liquids drawn off from the columns 18A and 18B and to recover the argon as a second product of the distillation.

[0087] In the plant 1, the use of two double columns 6A and 6B in parallel makes it possible to produce a large flow rate of oxygen gas OG.

[0088] Furthermore, that use of a dedicated denitrogenation column 18A, but above all a dedicated argon column 14A, for each double distillation column 6A and 6B makes it possible to limit the problems of regulating the operation of each of these columns. In particular, this regulating turns out to be much simpler and less expensive than if a single argon column and/or a single denitrogenation column were being used for the two double distillation columns 6A and 6B together.

[0089] It will be noted that controllable valves (not shown) are provided, particularly upstream and downstream of the mixing point 41 and the division point 54, in order to ensure that the columns 14 and 18 do indeed operate as dedicated columns. These valves make it possible to ensure that the flow rates of the fluids supplied to the columns 14 and 18, and drawn off from them, are such that the systems 2A and 2B operate substantially in the same way as if they were each operating on their own.

[0090] Since the system 3 is shared by the two air distillation systems 2A and 2B, the corresponding investment costs are therefore reduced.

[0091] Overall, therefore, the method carried out by using the plant 1 leads to investment and regulating costs which are relatively low.

[0092] According to a second embodiment, which is illustrated by FIG. 2, the auxiliary heat exchangers 32A and 32B are replaced by a common exchanger 32, which belongs to the system 3. The exchanger 32 is located downstream of the mixing point 41 and upstream of the division point 54.

[0093] This heat exchanger 32 is passed through, on the one hand, by the enriched gases coming from the argon columns 14A and 14B, which have previously been mixed in order to form a single stream, and on the other hand by the single stream of deoxygenated and dried gas coming from the drying unit 50.

[0094] This second embodiment makes it possible to reduce the required investment costs even further.

[0095] According to other embodiments (not shown), the compressor 42, the cooling devices 44 and 48, the deoxygenation unit 46, the phase separator 51 and the device 52 may respectively be replaced by two corresponding elements, one of which is dedicated to the system 2A and the other to the system 2B. Provisions will nevertheless be made to use at least a common compressor 42, or a common deoxygenation unit 46, or a common drying unit 50. It will be understood that these embodiments do, however, lead to a method for which the overall implementation costs are higher than those for the method in FIGS. 1 and 2. 

1-20. (cancelled).
 21. An air distillation method, comprising the steps of: a) distilling air in at least two double distillation columns, which operate in parallel, in order to form at least a first oxygen-enriched fluid and a first nitrogen-enriched fluid, wherein the double distillation columns comprising a higher-pressure column and a lower-pressure column; b) drawing off argon-rich fluid from the lower-pressure columns; c) distilling the argon-rich fluid in at least two argon columns, which operate in parallel, in order to form at least two streams of argon-enriched fluid and a second oxygen-enriched fluid; d) mixing the argon-enriched fluid streams downstream of the argon columns, e) compressing the argon-enriched fluid in at least one compressor, thereby producing a first compressed fluid; f) reacting hydrogen, with the oxygen contained in the first compressed fluid, in at least one deoxygenation unit, in order to deoxygenate it while producing water; g) passing the deoxygenated fluid through at least one drying unit in order to dry it, thereby producing a first dried fluid, wherein at least one element selected from the group consisting of the compressor, the deoxygenation unit, and the drying unit, is a common element which is used in order to compress or deoxygenate or dry the mixed fluids together, and h) distilling the first dried fluid in at least one denitrogenation column in order to form argon and a second nitrogen-enriched fluid.
 22. The method as claimed in claim 21, wherein the common element is the deoxygenation unit.
 23. The method as claimed in claim 21, wherein the common element is the drying unit.
 24. The method as claimed in claim 23, wherein the drying unit comprises a device for drying by adsorption.
 25. The method as claimed in claim 23, wherein the drying unit comprises a phase separator.
 26. The method as claimed in claim 21, wherein the common element is the compressor.
 27. The method as claimed in claim 26, wherein the mixed fluids are heated together in a common heat exchanger upstream of the compressor.
 28. The method as claimed in claim 23, wherein the dried fluids are cooled together in a common heat exchanger downstream of the drying unit.
 29. The method as claimed in claim 21, wherein the common elements are the drying unit and the compressor.
 30. The method as claimed in claim 29, wherein the mixed fluids are heated upstream of the compressor, and the dried fluids are cooled downstream of the drying unit, in a common heat exchanger.
 31. The method as claimed in claim 21, wherein a dedicated denitrogenation column, in which the respective deoxygenated and dried fluid is distilled, is used for each double distillation column and each argon column.
 32. An air distillation plant comprising: a) at least two double distillation columns, which operate in parallel, for distilling air while forming at least a first oxygen-enriched fluid and a first nitrogen-enriched fluid, the double distillation columns comprising a higher-pressure column and a lower-pressure column; b) means for drawing off an argon-rich fluid from the lower-pressure columns; c) at least two argon columns, which operate in parallel, for distilling the argon-rich fluid while forming at least two argon-enriched fluid streams and a second oxygen-enriched fluid; d) means for mixing the argon-enriched fluids downstream of the argon columns; e) at least one compressor for compressing the argon-enriched fluid; f) at least one deoxygenation unit for reacting hydrogen with the oxygen contained in the compressed fluid, in order to deoxygenate it while producing water; g) at least one drying unit for the deoxygenated fluid to be passed through in order to dry it, wherein at least one element selected from the group consisting of: the compressor, the deoxygenation unit and the drying unit, is a common element designed to compress or deoxygenate or dry the mixed fluids together; and h) at least one denitrogenation column for distilling the dried fluid while forming argon and a second nitrogen-enriched fluid.
 33. The plant as claimed in claim 32, wherein the common element is the deoxygenation unit.
 34. The plant as claimed in claim 32, wherein the common element is the drying unit.
 35. The plant as claimed in claim 34, wherein the drying unit comprises a device for drying by adsorption.
 36. The plant as claimed in claim 34, wherein the drying unit comprises a phase separator.
 37. The plant as claimed in claim 32, wherein the common element is the compressor.
 38. The plant as claimed in claim 37, further comprising a common heat exchanger, arranged upstream of the compressor, for heating the mixed fluids together.
 39. The plant as claimed in claim 34, further comprising a common heat exchanger, arranged downstream of the drying unit, for cooling the dried fluids together.
 40. The plant as claimed in claim 32, wherein the common elements are the drying unit and the compressor.
 41. The plant as claimed in claim 40, further comprising a single common heat exchanger, for heating the mixed fluids upstream of the compressor and cooling the mixed and dried fluids downstream of the drying unit.
 42. The plant as claimed in claim 32, further comprising, for each double distillation column and each argon column, a dedicated denitrogenation column for the respective deoxygenated and dried fluid to be distilled in it. 